Geographic Range

Habitat

Within the Amazon basin, A. gigas is found in several different types of habitat, such as the floodplain lakes of this region, the large tributaries of the Amazon river including the Rio Madera and the Rio Machado, and the varzea or forest. The pirarucu inhabits both white water and clear water. Much of the water that comprises the pirarucu's habitat is also oxygen deficient, as it is located in swampy areas of the rainforest.

Physical Description

The pirarucu is one of the largest freshwater fishes in the world. At one time, there were many individuals over 3 meters in length that weighed more than 150 kilograms. The scales on a pirarucu this size can reach 6 centimeters in length. However, there are few pirarucu this size, if any, that are living currently. The average size of this species has greatly reduced due to over-fishing, though it is still common to find pirarucu over 2 meters that weigh more than125 kilograms. The pirarucu is usually grey in color with an orange speckling near its posterior end. There are also two symmetrical fins on either side of the body at the posterior end. Interestingly, A. gigas has a bony or toothed tongue, which is the source of the title osteoglossomorph and a distinguishing character of those species in the order Osteoglossiformes.

Development

The female pirarucu is sexually mature at the age of five years old and are typically 160 centimeters in length at this point in their life.

(Queiroz, 1998)

Reproduction

Due to the geographic range that A. gigas inhabits, the animal's life cycle is greatly affected by the seasonal flooding that occurs. Half of the year the pirarucu experiences an abundance of water, which is a benefit to these aquatic organisms; however, the other half of the year the pirarucu experiences drought conditions. The pirarucu has adapted to this great fluctuation in many aspects of it's life, including reproduction. A. gigas lays it's eggs during the months of February, March, and April when the water levels are low. They build a nest approximately 50 cm wide and 15 cm deep, usually in sandy bottomed areas. As the water rises the eggs hatch and the offspring have the flood season to prosper, during the months of May to August. Therefore, the yearly spawning is regulated seasonally. A. gigas is a mouth-brooder.

A. gigas has been known to guard both the eggs and the offspring themselves. The parental care includes helping to aerate the water for it's offspring, which is a necessity for survival of the offspring in the oxygen-deficient waters of some habitats. Adults have the ability to exude a pheromone from their head to attract offspring and keep them in close proximity.

Food Habits

A. gigas is a predator that mainly eats other fish. If a bird or some other animal happens to be present, this large predator will also eat that animal. The pirarucu usually finds food near the top of the water because it is an obligate air breather that needs to surface every 10-20 min. However, the pirarucu is also capable of diving.

Predation

Economic Importance for Humans: Positive

A. gigas is hunted and utilized in many ways by local human populations. Pirarucu are harpooned or caught in large nets and the meat is said to be delicious. One individual can yield seventy kilograms of meat. In addition, the pirarucu's bony tongue is often used to scrape cylinders of dried guarana, an ingredient in a beverage, and the bony scales are used as nail files. This animal also appears in the pet trade, although to keep a pirarucu correctly requires a large tank and can prove quite difficult.

Economic Importance for Humans: Negative

There are no known adverse effects towards Homo sapiens.

Conservation Status

In 1976, the SUDEPE (Supertendencia do Desenvolvimento da Pesca) outlawed the killing of a pirarucu from October to March, during the low water season when this animal becomes so visible due to it's sheer size. Also the SUDEPE declared that the pirarucu has to be at least one and a half meters in length before it can be killed.

Other Comments

A. gigas was first named by Georges Cuvier in 1817. This animal is often called a living fossil due to it's archaic morphology. This fish has also been extremely successful in the Amazon. However, due to overfishing this animal is in danger of becoming extinct.

Contributors

William Fink (editor), University of Michigan-Ann Arbor.

Lewis Melfi (author), University of Michigan-Ann Arbor.

Glossary

Neotropical

living in the southern part of the New World. In other words, Central and South America.

bilateral symmetry

having body symmetry such that the animal can be divided in one plane into two mirror-image halves. Animals with bilateral symmetry have dorsal and ventral sides, as well as anterior and posterior ends. Synapomorphy of the Bilateria.

carnivore

an animal that mainly eats meat

chemical

uses smells or other chemicals to communicate

external fertilization

fertilization takes place outside the female's body

female parental care

parental care is carried out by females

fertilization

union of egg and spermatozoan

food

A substance that provides both nutrients and energy to a living thing.

freshwater

mainly lives in water that is not salty.

iteroparous

offspring are produced in more than one group (litters, clutches, etc.) and across multiple seasons (or other periods hospitable to reproduction). Iteroparous animals must, by definition, survive over multiple seasons (or periodic condition changes).

male parental care

parental care is carried out by males

motile

having the capacity to move from one place to another.

natatorial

specialized for swimming

native range

the area in which the animal is naturally found, the region in which it is endemic.

oviparous

reproduction in which eggs are released by the female; development of offspring occurs outside the mother's body.

pet trade

the business of buying and selling animals for people to keep in their homes as pets.

pheromones

chemicals released into air or water that are detected by and responded to by other animals of the same species

piscivore

an animal that mainly eats fish

rainforest

rainforests, both temperate and tropical, are dominated by trees often forming a closed canopy with little light reaching the ground. Epiphytes and climbing plants are also abundant. Precipitation is typically not limiting, but may be somewhat seasonal.

seasonal breeding

breeding is confined to a particular season

sexual

reproduction that includes combining the genetic contribution of two individuals, a male and a female

swamp

a wetland area that may be permanently or intermittently covered in water, often dominated by woody vegetation.

tactile

uses touch to communicate

tropical

the region of the earth that surrounds the equator, from 23.5 degrees north to 23.5 degrees south.

References

Goulding, M. 1980. Fishes and the Forest, Explorations in Amazonian Natural History. Berkeley: University of California Press.

Disclaimer:
The Animal Diversity Web is an educational resource written largely by and for college students. ADW doesn't cover all species in the world, nor does it include all the latest scientific information about organisms we describe. Though we edit our accounts for accuracy, we cannot guarantee all information in those accounts. While ADW staff and contributors provide references to books and websites that we believe are reputable, we cannot necessarily endorse the contents of references beyond our control.

This material is based upon work supported by the
National Science Foundation
Grants DRL 0089283, DRL 0628151, DUE 0633095, DRL 0918590, and DUE 1122742. Additional support has come from the Marisla Foundation, UM College of Literature, Science, and the Arts, Museum of Zoology, and Information and Technology Services.